European ground squirrel research

European ground squirrels (Spermophilus citellus) are obligate hibernators showing a strict annual schedule with only one litter per year and a pronounced fattening phase during summer to accumulate sufficient energy reserves for the hibernation period. We investigate reproductive strategies and relationships between ovarian activity and prehibernation fattening in ground squirrels kept in semi-natural outdoor enclosures within the natural habitat of the species. 

Reproductive timing and output

In contrast to other hibernating ground squirrel species, European ground squirrels reactivate ovarian activity after having weaned their litter and enter a second oestrus cycle in summer including spontaneous ovulation and an active luteal phase, reflected in oestradiol peaks followed by elevated progesterone secretion for several weeks. This oestrus cycle during the non-breeding season could improve reproductive performance in the following spring by initiating follicular development before hibernation, leading to an earlier conception date in the subsequent season. Early mating has been shown to be beneficial for both the female and her offspring in previous studies.

Luteal activity and the accumulation of body fat

Another benefit of the second oestrus cycle could be related to the elevated progesterone concentrations during the luteal phase in summer and prehibernation fattening. Adult females fatten up faster than males and relationships between progesterone secretion and the course and extent of fattening have been documented. We presently investigate faecal progesterone metabolites in females with and without reproductive effort and compare body mass changes, growth rates and the duration of the active season.

Glucocorticoid excretion patterns

Analyses of faecal cortisol metabolites as indicators of stress load have previously been validated for the species and are applied to investigate seasonal changes in behaviour and physiology. Another important issue is related to conservation as European ground squirrels are highly endangered in most parts of their distribution range. Therefore, management plans and reintroduction projects have been developed and implemented.

Information on the animals’ stress load during these activities via non-invasive measurements are highly valuable to identify critical phases and evaluate different approaches, like e.g. the soft release method in the context of reintroduction projects.

Researcher: Sandra Steinerberger, Isabelle Maiditsch, Michaela Brenner, Eva Millesi